At least 13 people are dead and several others were wounded after a gunman opened fire at the Washington Navy Yard on Monday, police said, spreading fear and chaos across the region as authorities sought to contain the panic.

The incident, in which the death toll rose almost hourly, represents the single worst loss of life in the District since an airliner plunged into the Potomac River in 1982, killing 78.

D.C. Police Chief Cathy L. Lanier and Mayor Vincent C. Gray announced the mounting number of casualties in a series of news conferences. The suspected shooter, identified by the FBI as Aaron Alexis, 34, living in Fort Worth, is among the 13 dead. Alexis was a military contractor, one official said.

But even hours after the rampage began, it was still unclear whether the shooting was the act of a lone gunman, or if other shooters were involved. Lanier initially said authorities were looking for two more potential shooters dressed in military style clothing. But shortly after she announced a detailed description of two suspects, city officials said one had been located and cleared.

Gray said no motive is known yet. He said there is no reason to believe it was an act of terrorism, though he added that he could not rule it out.

Gray said that in addition to those killed, about a dozen people were hurt. It was not clear whether those people were shot or suffered other injuries, he said.

Lanier described the other possible suspect, who has not been located, as a black man in his 40s with gray sideburns, wearing an olive-drab military-style uniform. He, and the man who was cleared, came under suspicion when they were seen on surveillance videos.

Police are asking anyone with information on the suspect to call 202-727-9099.

Alexis was armed with an assault rifle and a handgun, two law enforcement officials said. One said he also had a shotgun. One official said all the weapons have not been accounted for.

The first, sketchy details about the suspect offered few hints about what may have gone wrong.

Alexis grew up in Brooklyn with his mother, Sarah, and father, Anthony Alexis, according to his aunt Helen Weeks.

“We haven’t seen him for years,” Weeks said of her nephew in a telephone interview. “I know he was in the military. He served abroad. I think he was doing some kind of computer work.”

Alexis spent nearly four years in the Navy as a full-time reservist from May 2007 until he was discharged in January 2011, according to a summary of his personnel records released by Navy officials at the Pentagon.

The officials said they were still researching whether Alexis had been employed as a defense contractor or a civilian employee of the Navy, and were uncertain if he was assigned to work at the Navy Yard.

He achieved his final rank of Aviation Electrician’s Mate 3rd Class in December 2009. Officials said they did not immediately know the reasons for his discharge.

The carnage began around 8 a.m. when the U.S. Navy said that three shots were fired at Building 197, headquarters of the Naval Sea Systems Command. About 3,000 people work in the building. As the noise that some thought sounded like construction work continued, the realization set in that a gunman was firing on them.

Rick Mason, a program management analyst who is a civilian with the U.S. Navy, told the Associated Press that a gunman was shooting from a fourth floor overlook in the hallway outside his office. He said the gunman was aiming at people in the building’s first floor cafeteria.

Terry Durham said that as she and co-workers were evacuating, she saw a man down the hall raise a rifle and fire toward them, hitting a wall.

“He didn’t say a word,” said her co-worker, Todd Brundage.

One man who said he was at his desk on the second floor when the shooting began recalled hearing a loud noise “l(fā)ike someone dropping an old metal desk.” The man, who declined to give his name, said there was a pause, then several noises close together and he realized the danger: “There’s a shooter in the building. I started walking toward the door and I heard people running down the hall.”

Employees described the chaos, as a fire alarm sounded and people shouted, “Where is he? Where is he?”

Gregory Dade, a Navy contractor, said he and a co-worker locked themselves in a second floor office of Building 197 as soon as the shooting went on, in fits and stops. Dade, called it “terrifying.”

He heard a woman scream, glass crashing and a series of gun shots. Then he heard shouting: “Get down! Get down! This is the police.”

Finally, about 11 a.m., he and a co-worker made a break for it.

At an exit, they noticed a trail of blood running to the next building.

Tim Jirus, a Navy commander who works in Building 197, said that as he was evacuating the building he saw a co-worker who had been shot getting into a police car, and heard more shots fired from inside his workplace.

A far worse sight lay just ahead. Jirus went to an alley where he thought he would be safe, and talked briefly with a man there about what was going on. Jirus said he heard two gunshots, loudly echoing off the building. It caused him to spin around to look for the source of the noise. But when he turned back, he looked down and saw the man he had been conversing with lying on the ground, shot in the head.

Uncertain where the shooter was, he ran.

“I was just lucky,” he said. “The other person was shorter than me. There were two shots, he got that guy, he didn’t get me. . . . The randomness of it — standing right next to me, one person gets shot.”

At least two police officers were among those shot. Police on the scene said one is a D.C. police officer who was shot twice in the leg and was evacuated to a hospital. Lanier said he was in stable condition after engaging the shooter with gunfire. The other was a base officer. The D.C. officer, was conscious at MedStar Washington Hospital Center and his chances for survival were good, hospital officials said.

Janis Orlowski, the chief medical officer at Washington Hospital Center, said three victims in all were brought to the center, all in critical condition but alert, responsive and able to talk with doctors. The victims were also able to speak briefly to law enforcement officers before undergoing surgery or treatment, she said.

The other two victims at the hospital were female civilians, Orlowski said at a news conference. All are likely to survive.

The impact of the incident rippled across town, forces schools, offices and homes into an enforced lockdown.

Senate buildings on Capitol Hill went on lockdown at about 3 p.m., with no one allowed to enter or leave the building, though it was partially lifted toward the end of the day to allow staffers to go home.

The Nationals, whose ballpark is near the Navy Yard, postponed a Monday night game. Instead, they will play a double header Tuesday at 1 p.m. and 7 p.m.

Ten public and charter schools and a public school administration building in the District went on lockdown, and flights out of Reagan National Airport were briefly halted, causing delays even after they began departing again.

Adm. Jonathan W. Greenert, the chief of Naval Operations, was evacuated from his residence at the Navy Yard complex shortly after the first report of shots fired, Navy officials said.

Greenert, a four-star admiral and member of the Joint Chiefs of Staff, was safely evacuated to the Pentagon along with his wife, Darleen, said Cmdr. Ryan Perry, a Navy spokesman.

Police closed the 11th Street Bridge as well as M Street SE between Second and Fourth streets SE because of the shooting. Entrances to the Navy Yard Metro station remain open.

As helicopters circled overhead and emergency vehicles continued to rush to the scene, crowds of onlookers gathered on sidewalks and at a construction site near the Navy Yard, but police pushed them back, yelling at them to keep a distance from the grounds.

President Obama on Monday expressed sympathy for the victims of the shooting and said justice must be sought.

“I’ve made it clear to my team that we want the investigation to be seamless, so that local and federal authorities are working together,” he said.

As a long day drew to a close, weary and stunned Navy personnel filtered into Capitol Hill in their tan uniforms, blue camouflage fatigues and civilian clothes, many of them saying little, just wanting to get home after a day spent running or hiding, and then waiting.

Tom Dick-Peddie, 46, was at work in another building in the Navy Yard and said they were on lockdown for about an hour and a half, then they were evacuated to another building. Shortly after 3 p.m. they were allowed to leave.

Kate O’Neill of Arlington and Stephanie Cates-Harman of Columbia, who work in the office of the general counsel, said their office had been ordered to shelter in place until 2 p.m. While some people were very upset, and others were calm, and tried to contact relatives to assure them that they were okay.

“Texts were going fast and furious,” O’Neill said.

9月16日，位于美國首都華盛頓的海軍海洋系統(tǒng)司令部發(fā)生一起惡性槍擊案，造成至少13人死亡、十多人受傷。這是自1982年致死78人的波托馬克河空難以來，華盛頓地區(qū)發(fā)生的死亡人數(shù)最多的單起事件。目前，唯一嫌犯的身份被確定為海軍退伍軍人阿龍·亞歷克西斯，他已在現(xiàn)場被擊斃。

***目擊者講述案發(fā)經(jīng)過

當(dāng)天早晨8點左右，海軍海洋系統(tǒng)司令部總部傳來三聲槍響，當(dāng)時大約有3000人在總部大樓里工作。起初聽見異響時，部分工作人員以為是有建筑工程正在施工，然而事實上，一名兇徒將槍口對準(zhǔn)了他們。

里克·梅森是一名項目管理分析師，他碰巧目睹了案發(fā)的經(jīng)過，“我的辦公室在四樓，我看見一名槍手站在辦公室外的走廊里向下張望。然后，他拿起槍向一樓咖啡廳的人們掃射”。特里·德拉姆說，她和同事從辦公樓撤離時，她看見一名男子站在大廳里、舉起一把槍向他們開火，子彈射到了墻壁上�！八�一個字也沒說，”德拉姆的同事托德·布倫戴奇在一旁補(bǔ)充道。

另一名在二樓辦公的工作人員回憶稱，槍擊開始時他聽見了一聲巨響，“就像有人丟下了一張舊金屬桌”。“短暫沉默后，又有幾聲連續(xù)的噪音傳來，這時我才意識到危險了：大樓里有一名槍手！我朝門外跑去，走廊里響起雜亂的腳步聲和人們的驚呼聲‘他（槍手）在哪兒？他在哪兒？’”

海軍承包商格雷戈里·戴德說，聽見槍聲后，他和一名同事立刻把自己鎖在二樓辦公室里。“當(dāng)時太嚇人了，”戴德說，他聽見女人的尖叫聲、玻璃碎裂的聲音和一連串的槍響，“然后有人高喊‘趴下！趴下！我們是警察”。終于，噩夢在11點左右結(jié)束了，戴德和同事走出總部大樓時，看見有血跡一直通向隔壁的建筑。

而另一名海軍承包商蒂姆·吉瑞斯經(jīng)歷了更加驚險的一幕。聽見槍響后，吉瑞斯迅速跑進(jìn)一條走廊，他以為自己安全了，就同旁邊的一名男子聊起當(dāng)下的狀況�！拔衣犚娏藘陕晿岉�，于是自然而然地四處張望尋找聲音的來源。突然，我看見地上躺了一個人，就是剛才和我說話的那個人，他的頭部中槍了、鮮血不斷涌出，”吉瑞斯回憶說，“我不知道槍手在哪兒，我拔腿就跑。我只是走運，兇手開了兩槍，他打中那個男人、卻沒能打中我�！�

***嫌犯身份確定

目前，嫌犯的身份已被美國聯(lián)邦調(diào)查局（FBI）確認(rèn)為阿龍·亞歷克西斯。亞歷克西斯今年34歲，他隨父母在紐約市布魯克林區(qū)長大，生前居住在得克薩斯州沃斯堡市。“我們好幾年沒見過他了，”亞歷克西斯的嬸嬸海倫·威克斯接受電話采訪時說，“我知道他在軍隊，還去過國外服役，我以為他做的是與電腦相關(guān)的工作�！�

自2007年5月起，亞歷克西斯曾在美國海軍服役近4年，直至2011年1月退役。美國官員稱，他們?nèi)栽谡{(diào)查亞力克西斯退役后是否受雇成為一名國防承包商或者海軍的文職雇員，他們不確定亞歷克西斯是否被安排到海軍海洋系統(tǒng)司令部工作。

據(jù)兩名執(zhí)法人員透露，行兇時亞歷克西斯手持一支沖鋒槍和一把手槍。也有人說，兇徒還有一把散彈獵槍。不過，上述說法均尚未被證實。

***槍擊案是一人所為

槍擊案發(fā)生后，華盛頓當(dāng)局舉行了一系列新聞發(fā)布會，對外公布案件進(jìn)展。

當(dāng)?shù)貢r間16日，華盛頓警方負(fù)責(zé)人凱茜·拉尼爾宣布，此次惡性槍擊案是“一人所為”，不存在其他嫌犯。此前，拉尼爾曾宣稱警方正在搜索兩名潛在嫌犯，她還公布了這兩名潛在嫌犯的外貌特征。拉尼爾還表示，之前向海軍海洋系統(tǒng)司令部的工作人員以及司令部周邊民眾發(fā)布的“就地避難”指令已被解除。

華盛頓市長文森特·格雷在新聞發(fā)布會上公開了部分遇難者的身份信息。據(jù)悉，遇難者的年齡從46歲至73歲不等，有關(guān)部門正在向遇難者家屬告知這一不幸的消息。格雷稱，目前還不清楚槍手的行兇動機(jī)，“但沒有理由認(rèn)為這是一起恐怖主義行為”，不過他補(bǔ)充道也不能排除這種可能性。

***奧巴馬厲聲譴責(zé)

此次槍擊案已對華盛頓造成巨大影響。距離事發(fā)地點僅6分鐘車程的國會參議院在16日下午3時關(guān)閉，不允許任何人進(jìn)入或者離開。不過當(dāng)天晚些時候，參議院的大門重新開放，議員們獲準(zhǔn)回家。備受關(guān)注的本地棒球比賽宣布推后一天舉行，將在17日連賽兩場。

除此之外，還有10所公立和特許學(xué)校以及一棟公立學(xué)校行政樓被封鎖。在華盛頓里根國家機(jī)場，飛機(jī)被暫時禁止飛離，導(dǎo)致機(jī)場出現(xiàn)航班滯留晚點的現(xiàn)象。

16日，美國總統(tǒng)奧巴馬嚴(yán)辭譴責(zé)美海軍海洋系統(tǒng)司令部槍擊案是“懦夫行為”，發(fā)誓將展開全面調(diào)查，把兇手繩之以法。奧巴馬稱，槍擊案發(fā)生后，他一直在聽取情況匯報，“我已發(fā)出明確指示，要求聯(lián)邦和地方當(dāng)局密切合作，展開無縫調(diào)查，竭盡全力將制造這起懦夫行為的人繩之以法”。